The present invention relates to ink for a ball pen which is called medium viscosity ink, neutral ink, gel ink, aqueous gel ink or the like, and to a ball pen using the ink for a ball pen, more specifically the present invention relates to ink for a ball pen which consumes much ink, that is, a ball pen for writing thick and bold letters and a bold ball pen using the ink for a ball pen.
Various types of ball pen have been proposed conventionally.
For example, there is provided a ball pen filled with ink using water or an aqueous medium as a solvent and dye or pigment as a colorant. Hereinafter the ink is referred to as xe2x80x9caqueous inkxe2x80x9d and the ball pen as an xe2x80x9caqueous ball pen.xe2x80x9d
The aqueous ball pen shows so low viscosity that it may advantageously write smoothly at low writing-pressure. On the other hand, however, it is likely to occur that, when the pen is exposed to vibration or impact, the ink leaks from the point of pen-tip (hereinafter referred to as xe2x80x9cdirect flowxe2x80x9d) and that the stability of the ink-flow rate decreases (hereinafter referred to as xe2x80x9cfluctuatingxe2x80x9d) by the air involved from the point of the pen-tip. Further, the aqueous ball pen also has a defect that lines written therewith tend to be blurred.
Meanwhile, there is also provided a ball pen filled with ink using an organic medium as a solvent and dye or pigment as a colorant. Hereinafter the ink is referred to as xe2x80x9coil-based inkxe2x80x9d and the ball pen as an xe2x80x9coil-based ball pen.xe2x80x9d
Since the oil-based ball pen uses highly viscous ink, it is free from above-mentioned defects as seen in the aqueous ball pen. However, it has a defect that high writing pressure is needed for writing, resulting in a heavy writing feeling. Further, it also has a defect that it is likely to make the pen-tip and the paper surface dirty with ink blots (hereinafter referred to as xe2x80x9cblottingxe2x80x9d).
There has recently been provided a ball pen filled with ink using water or a water-soluble medium as a solvent, dye or pigment as a colorant and, further, a pseudoplasticizing so that the ink may have pseudoplasticity. Hereinafter the of ink is referred to as xe2x80x9caqueous gel inkxe2x80x9d and the ball pen as an xe2x80x9caqueous-gel ball pen.xe2x80x9d
Here, pseudoplasticity is a property showing non-flowability in a static state and also showing flowability when a shearing force is applied.
The aqueous gel ink shows non-flowability in an ink reservoir as well as the oil-based ink while it shows flowability like aqueous ink near the point of the pen-tip where a shearing force is applied to the ink due to the rotation of the ball.
Accordingly, the aqueous-gel ball pen has both the advantage of an aqueous ball pen and that of an oil-based ball pen. That is, the aqueous-gel ball pen has advantages that it can write smoothly at a low writing pressure, that the lines written therewith are hard to blur and that the blotting is less likely to occur.
Actually, however, the production of the aqueous-gel ball pen is not so easy.
For example, a pen-tip containing a ball with a diameter of 0.5 mm and a pen-tip containing a ball with a diameter of 0.7 mm are different in the clearance between the ball and a holder as well as in the shearing force applied to the ink caused by rotation of the ball. Therefore, if aqueous gel ink suitable for one of these two types of pen-tips is used for the other, the direct flow and fluctuating will occur or the blotting will occur.
Accordingly, the viscosity of the aqueous gel ink should be adjusted in accordance with the pen-tip to be used.
Further, an aqueous-gel ball pen with which relatively thick and bold letters (hereinafter referred to as an xe2x80x9caqueous-gel bold ball penxe2x80x9d) can be written is desired recently.
The aqueous-gel bold ball pen uses a ball with a diameter of 0.9 mm or more so as to be adapted for writing bold letters.
Further, the aqueous-gel bold ball pen is formed to have a relatively large clearance between the ball and the holder since, only by enlarging the diameter of the ball, the written line, which can be wider, appears pale in color.
Moreover, the aqueous-gel bold ball pen needs so much ink to be supplied to the pen-tip as to account for the amount according to the larger diameter of the ball and the amount according to the larger clearance between the ball and the holder.
Specifically, ink should be supplied to the pen-tip so that the ink-consumption value per unit area may fall within a range on the order of 0.64 to 1.6 mg/cm2.
This ink-consumption corresponds to as much as 1.5 to 3 times that of a conventional aqueous-gel ball pen.
When the ink-consumption is increased, however, the ink transferred onto the paper surface becomes hard to dry.
From this reason, water content in the ink is made relatively high in such an aqueous-gel bold ball pen for the purpose of enhancing quick-drying property of the ink transferred onto the paper surface.
Relatively high water content in the ink improves the quick-drying property of the ink transferred onto the paper surface while it leads to a disadvantage that the point of the pen-tip is easy to dry.
Further, when the water content in the ink is made relatively high, friction resistance between the ball and the holder increases, which leads to a disadvantage that the writing feeling is deteriorated.
That is, such an attempt to improve the quick-drying property of the ink transferred onto the paper surface results in the fact that the point of the pen-tip is easy to dry and that the writing feeling is deteriorated.
It is very difficult to strike a balance between the quick-drying property of the ink transferred onto the paper surface and the non-drying property of the point of the pen-tip while maintaining good writing feeling.